21396660 has 72 divisors (see below), whose sum is σ = 63527520. Its totient is φ = 5366016.

The previous prime is 21396649. The next prime is 21396667. The reversal of 21396660 is 6669312.

It is a happy number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21396667) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 156112 + ... + 156248.

Almost surely, 2^21396660 is an apocalyptic number.

21396660 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21396660, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31763760).

21396660 is an abundant number, since it is smaller than the sum of its proper divisors (42130860).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21396660 is a wasteful number, since it uses less digits than its factorization.

21396660 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 305 (or 166 counting only the distinct ones).

The product of its (nonzero) digits is 11664, while the sum is 33.

The square root of 21396660 is about 4625.6523864208. The cubic root of 21396660 is about 277.6186652621.

The spelling of 21396660 in words is "twenty-one million, three hundred ninety-six thousand, six hundred sixty".